This application is a continuation-in-part of co-pending U.S. application Ser. No. 08/726,680, filed Oct. 7, 1996.
The present invention relates to fluid mixing systems, and more particularly, to a mixing module and method for generating a horizontal fluid flow in a reactor vessel or other flow channel, which vessel or flow channel may include an associated aeration system.
Although horizontal fluid flow is desirable in many fluid mixing systems, the generation of a horizontal fluid flow is especially important in the treatment of water, sewage and like waste liquids in plug flow reactors or oxidation ditches to promote the mixing and agitation of suspended solids. Conventionally, the treatment of water, sewage and like waste liquids in such reactors has utilized multiple side entry or horizontally-oriented turbine agitators. Such agitators require a relatively large amount of horsepower, specific positioning within the reactors and fine adjustments to generate the requisite fluid flow and agitation.
Plug flow reactors have also utilized horizontally-oriented, submersible turbine agitators. Such submersible agitators must be removed from within a plug flow reactor for servicing utilizing various lifting devices. Furthermore, agitators which are entirely submerged require expensive mechanical seals, moisture detectors and housings since the electrical and mechanical components of the agitators are submerged.
In conventional plug flow reactors, the diameter of the impellers on the turbine shafts of the agitators are often limited by the fluid depth of the reactors since the diameter of a side entry or horizontally-oriented turbine extends in a depth-wise direction.
The use of top-entry vertical turbine agitators is known in the art for batch or continuous fluid reactors. For example, U.S. Pat. No. 5,046,856 to McIntire discloses the use of a series of top-entry vertical turbine agitators in a series of tanks wherein at least one of the tanks overflows into another. U.S. Pat. No. 4,566,971 to Reimann et al. teaches the use of a top-entry vertical turbine agitator in a continuous flow-stirred tank. Such top-entry agitators are characterized by mechanicals which are above the liquid level of the associated vessel, and have a vertical shaft extending down into the vessel. However, such "top-entry" vertical turbine agitators have not been used to generate directed, horizontal flow streams.
In reactor vessels or other flow channels which include an aeration system, conventional agitators or mixers must be carefully positioned with respect to the aeration source. For example, horizontal flow losses can be experienced if the mixer or agitator is placed at an upstream position which is close to the aeration source because the aeration source tends to generate a "wall" of gas bubbles. Further, untrue running of the mixer or agitator can occur if the mixer or agitator is placed at a downstream position which is closed to the aeration source due to bubbles being suctioned into the mixer or agitator.
Accordingly, there is a need for a highly efficient fluid mixing system which uses minimal horsepower, provides greater uniformity of velocity profile versus fluid depth and is easily serviced and maintained. There is also a need for a horizontal flow generator which is less sensitive to positioning relative to aeration sources in mixing systems.